This program investigates how the body controls its internal environment. The steady state of the Earth’s biosphere is compared to that of the human body. An automated greenhouse and a computerized inventory system demonstrate how negative feedback loops use detection and response to maintain their own balanced states. The regulation of body temperature in response to extreme heat and cold is explored both in a sauna and on a mountain slope. The roles of the pancreas and liver in controlling blood glucose levels are described. And the control of water concentration at the cellular level and waste filtration via the kidneys are explained. The impact of alcohol consumption on temperature regulation and water management is also considered. (20 minutes)